Re: [PATCH] x86/boot: Fix BIOS memory corruption on certain IBM systems

[George Dunlap <george.dunlap@eu.citrix.com>]

On 12/03/2013 08:34 PM, Andrew Cooper wrote:
> IBM System x3530 M4 BIOSes (including the latest available at the time of this
> patch) will corrupt a byte at physical address 0x105ff1 to the value of 0x86
> if %esp has the value 0x00080000 when issuing an `int $0x15 (ax=0xec00)` to
> inform the system about our intended operating mode.
>
> Xen gets unhappy when the bootloader has placed it's .text section in over
> this specific region of RAM.
>
> After dropping into 16bit mode, initialise as much state as we possibly can to
> sane values. This includes 0 for all the GPRs and %cs for %fs and %gs which
> would otherwise be unreal segment selectors.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Keir Fraser <keir@xen.org>
> CC: Jan Beulich <JBeulich@suse.com>
> CC: George Dunlap <george.dunlap@eu.citrix.com>
>
> ---
>
> George:
>   * This fixes a memory corruption issue, so counts towards both #1 and #2 as
>     far as a freeze exception goes.

The general rule during the code freeze is that bug fixes are exempt 
from needing a freeze exception, unless the maintainers think that it's 
particularly risky.  I suppose one could quibble about whether this is a 
"bug fix" or a "work-around for broken BIOS" though, so just in case:

Release-acked-by: George Dunlap <george.dunlap@eu.citrix.com>